The invention relates to a method for operating an internal combustion engine and to an internal combustion engine.
It is known to operate internal combustion engines with a gaseous fuel, in particular in a dual-substance mode which is also referred to as a bi-fuel mode. It has been shown that the chemical composition of gases available for the operation of such an internal combustion engine is subject to extreme fluctuations. Characteristic values which are characteristic for a quality of the gaseous fuel—such as, for example, the heating value or the stoichiometric air ratio—are subject to fluctuations of up to or even greater than 50%. In order to provide for a controlled operation of the internal combustion engine, a reliable characterization of the gaseous fuel which is used is therefore necessary. In principle, its composition could be ascertained by means of a gas chromatograph and/or a chemical analysis, but corresponding sensors are out of the question for use in the field, due to reasons related to cost and complexity. In principle, it is also possible to measure the combustion process directly in the internal combustion engine. This can take place, for example, by means of cylinder pressure indication or a combustion chamber-side temperature measurement. This approach is very expensive, however, and it is not possible to retrofit existing diesel engines with suitable sensors for the dual-substance mode.